Sulfolane solvent recovery from water wash



March 7, 1967 c. H. DEAL, JR 3,308,059

SULFOLANE SOLVENT RECOVERY FROM WATER WASH Filed March 31, 1965 [AQUEOUS SULFOLANE r NON -AROMAT|CS INVENTOR! CARL H. DEAL,JR.

HIS ATTORNEY United States Patent Ofifice 3,398,059 Patented Mar. 7, 1967 This invention relates to a process for the extraction and recovery or aromatic hydrocarbons from a liquid hydrocarbon mixture. More particularly, the invention relates to an improved process employing a sulfolane as an extractive solvent for separating kerosene-range aromatics.

everal processes for the extraction and recovery of aromatic hydrocarbons from liquid hydrocarbon mixtures have already been proposed. Various high-boiling, aromatic selective solvents have been suggested, among those are diethvlene glycol, dipropylene glycol and sulfolane. Of considerable expense in recovering aromatics or producing a low aromatic raffinate by extraction and in separating solvent from the product stream through water washing is the recovery of solvent from the solvent-containing water wash, especially when the aromatic hydrocarbons include those in the kerosene boiling range where the boiling points of the aromatics become especially close to that of the high-boiling solvents. e.g., sulfolane. It would be of advantage to provide an eflicient method by which the water and solvent could be separated without expensive distillation.

It is the principal object of this invention to provide an improved method for the separation of aromatic hydrocarbons from non-aromatic hydrocarbons. A further object of this invention is to furnish a process for the economic separation of sulfolane from an aqueous solution thereof. The advantages of the present invention and its practice will be better understood from the detailed description made with reference to the accompanying drawing wherein the sole figure is a schematic representation of 'a preferred system for the practice of the improved process.

Now, in accordance with this invention, it has been found that an aqueous sulfolane solution can be treated to separate the sulfolane therefrom by passing the solution in countercurrent contact with a hydrocarbon, e.g., the incoming feed to a liquid-liquid extraction system. In the conventional process, a kerosene range hydrocarbon mixture is introduced into one end of an extractor and passed in countercurrent contact with sulfolane introduced near the other end. The rafiinate phase containing primarily the non-aromatic hydrocarbons is passed to a raffinate wash column wherein it is water-washed to separate any sulfolane removed from the primary extractor with the non-aromatic railinite. The fat sulfolane solvent containing primarily the aromatics is passed from the extractor to an extractive stripping column wherein any light hydrocarbon removed with the sulfolane is overheaded and refluxed to the extractor for further separation. The bottoms product from the extractive stripping column, containing sulfolane and aromatic hydrocarbons is passed to a stripping column from wherein the aromatic hydrocarbons are removed overhead while the sulfolane is removed as bottom product and returned to the extractor. The aromatic hydrocarbons, containing a portion of the sulfolane, which increases as the voltatilities of the aromatics approach that of the sulfolane, is waterwashed to remove the sulfolane before it is recovered as product. This aqueous extract containing the solvent is distilled to separate sulfolane and water for recycle. With the present invention, the sulfolane containing water wash (1) of the non-aromatic ratfinate separated in the extractor and/ or (2) of the aromatics obtained overhead from the stripping column, are passed to a pre-wash column wherein these aqueous solutions flow in countercurrent contact with hydrocarbon feed. The feed which selectively extracts the sulfolane, is then introduced into the main extractor while the stripped aqueous phase can be passed as washing liquid to the raffinate washing zone and/or the aromatic washing zone. A portion of this feed washed water phase may, however, be distilled and used in a final wash of the product hydrocarbons.

The sulfolane solvents of the invention may be made by condensing a conjugated diolefin with sulfur dioxide and then subjecting the resulting product to hydrogenation, alkylation, hydration and/or other substitution or addition reactions. A 2-sulfolene may be made similarly by isomerizing instead of by hydrogenating the product resulting from condensing a conjugated diolefin with sulfur dioxide. Unsubstituted sulfolane, the preferred sulfolane solvent in the process of the invention, has the formula:

/s (1H CH2 CHZCII2 and 2sulfolene has the formula:

Other solvents which have high selectivity for separating aromatics from non-aromatic hydrocarbons are: Z-methylsulfolane, 2,4-dirnethylsulfolane, 2,4-dimethyl-4-sulfolane, methyl 3-sulfolanyl ether, ethyl-3-sulfolanyl sulfide, methyl-aryl-3-sulfolany1 ether, n-aryl-3-sulfolanyl amine, 3-sulfolanyl acetate, and others. Although the use of sulfolane solvents is a preferred embodiment of the invention other suitable solvents such as diethylene glycol, various polyethylene glycols and mixtures thereof can be employed.

In a preferred embodiment of the invention the sulfolane solvents for use in the extractive stripping process have the general formula:

where R can be a hydrogen atom, an alkyl group having up to 8 carbon atoms, an aryl rtdical having up to 8 carbon atoms, an allroxy radical having up to 8 carbon atoms, an arylalkyl radical having up to 8 carbon atoms, an ralkhydroxy having up to 8 carbon atoms or mixtures thereof. In a particularly preferred embodiment, all Rs are hydrogen.

The present process can be applied to feed stocks having a wide or a narrow boiling range. It is especially suitable for separating aromatics from catalytically reformed gasolines, such as hydroformates and platformates or from fractions thereof.

In carrying out the process according to the invention, the volumetric ratio of sulfolane to hydrocarbon feed should be between 3:1 and 821, preferably between 4:1 and 6:1, whereas the ratio of the amount of top product returned from the stripping zone to the extraction system to the amount of hydrocarbon feed should be between 0.211 to 0.7:1, preferably between 03:1 and 05:1.

The feed to the aromatic extractor may be introduced at an intermediate point, but it is generally preferred to introduce it at or at least near that end of the extraction system at which the aromatic-rich extract phase is withdrawn, because in that case the best compromise between product purity and recovery is usually realized. Suitable inlet points are at the ends of the extractor or at the second theoretical stage, the latter embodiment being preferred because in that case the purity is distinctly higher whereas the recovery is only slightly decreased.

Referring to the single figure, the shown embodiment is a preferred system for the continuous separation of non-aromatics from aromatics employing sulfolane as the selective solvent. A hydrocarbon feed mixture is introduced via line 1 into pre wash column 3 from which a substantially pure water stream is removed via line 5. The water was introduced via line 7 as part of an aqueous sulfolane-containing stream to column 3, wherein it passes in countercurrent contact with the hydrocarbon feed which selectively extracts sulfolane from the aqueous sulfolane-containing stream. A feed/sulfolane mixture is removed overhead via line 8 and is passed to the lower end of extractor 9 wherein it flows in countercurrent contact with the sulfolane solvent introduced into the upper end of extractor 9 via line 11.

The hydrocarbon feed stream, stripped of its aromatic portion is removed overhead via line 13. A fat solvent stream containing an aromatic portion of the feed and a minor amount of the non-aromatic hydrocarbons is removed via line 15 and passes to a middle portion of extractor stripper '17 from which a raffinate containing the non-aromatic hydrocarbons is returned via line 19 to the bottom of extractor 9'. The bottoms portion containing sulfolane and aromatic hydrocarbons is passed via line 21 to stripping column 2'3 from which an overhead fraction containing aromatic hydrocarbon and a minor portion of sulfolane is removed via line 25. The sulfolane bottoms are recycled via line ill to the upper portion of extractor 5.

The non-aromatic hydrocarbon ralfinate removed via line M from extractor 9 passes to the lower portion of ralfinate wash zone 27 wherein it is countercurrently treated with :Water introduced near the top of zone 27 through line 28. The stripped non-aromatics are recovered via line 29 while the sulfolane/water solution is removed via line 3 1 and returned via line 7 to pre-wash column 3. The aromatic stream, containing a minor portion of sulfolane, is removed overhead from 23 and is passed via line 25 into extract wash zone 32 where it is countercurrently contacted with water introduced via line 33. The water Washed aromatics are recovered via line 35 while the sulfolane-containing water wash is removed via line 7 and returned to pre-wash column 3.

Although this specific embodiment illustrates separate water wash means 2% and 36, it is a part of this invention to recycle the water removed via line 5 from pro-wash column 3 to line 28 and to pass in series the Water/sulfolane removed via 31 as makeup water to zone 32 via line 36. This is essence would produce a closed loop of the water circlating in the system.

A still further modification would involve distilling a portion of the water removed via line 5 and returning only the distillation product via line 28 and/ or line 33. The remainder of the solvent-containing wash stream of line .5 would be introduced at some intermediate point in column 27 and/ or 32 via lines 36 and 37, respectively.

The drawing is merely diagrammatic and is not intended to fully show all the component parts of the equipment which one skilled in the art will routinely design for the operation. Indeed, the showing of an element or piece of equipment does not mean that all such or similar pieces of equipment which may or can be designed by one skilled in the art in possession of this disclosure cannot be utilized as substitution therefore. Likewise, the omission of an element which one skilled in the art may include in an actual unit does not mean that such a piece of equipment is intended to be omitted simply because it does not appear in the drawing. Sufiice to say, the drawing is for illustrative purposes, as in the description thereof.

I claim as my invention:

1. in a process for the extraction and recovery of aromatic hydrocarbons with a sulfolane solvent, from a liquid hydrocarbon mixture containing aromatic and non-aromatic hydrocarbons, wherein the sulfolane is water-Washed from at least one of a sulfolane-containing non-aromatic raflinate and a sulfolane-containing aromatic product, the improvement comprising:

(a) contacting the resulting sulfolane-containing water Wash in a pre-wash zone with said hydrocarbon feed, thereby extracting the sulfolane from the sulfolanecontaining water-wash by said feed, and

(b) recovering a water phase of substantially reduced sulfolane content.

2. In a process for the extraction and recovery of aromatic hydrocarbons from a liquid hydrocarbon mixture containing aromatic and non-aromatic hydrocarbons comprising:

(a) passing said mixture in countercurrent flow with a s ulfolane solvent in a multistage extraction zone whereby a sulfolane extract phase enriched in aromatics is obtained;

(b) withdrawing said extract phase from the extraction zone and passing it to an extractive stripping zone wherein non-aromatic hydrocarbons and a minor amount of sulfolane are removed overhead;

(0) withdrawing as bottoms, a sulfolane-aromatic hydrocarbon mixture and passing it to a stripping zone wherein the aromatic hydrocarbons along with the minor amount of sulfolane are removed overhead, whereby the remaining sulfolane is recovered and separated as bottoms; i

(d) separately Water-Washing the sulfolane-non-aromatic mixture removed overhead from step (b) and the sulfolane-aromatic mixture removed overhead from step (c), thereby extracting sulfolane into aqueous wash streams, the improvement comprising recycling at least one of the sulfolane-containing water-wash streams in countercurrent contact with said hydrocarbon feed mixture in a pre-washzone, separating water as a separate phase from said prewash zone and returning the sulfolane-hydrocarbon mixture to the extraction zone.

3. A process in accordance with claim 2 wherein the suifolane-containing water-Wash stream obtained by treatment of the sulfolane-nonnromatic mixture is recycled and passed in countercurrent contact with said hydrocarbon feed.

4. A process in accordance with claim 2 wherein the sulfolane-containing water-wash stream obtained by treatment of the sulfolane-aromatic mixture is recycled and passed in countercurrent contact with said hydrocarbon feed.

5 A process in accordance with claim 2 wherein part of the water separated in the pro-Wash zone is distilled.

6. A process in accordance with claim 1 wherein the suifolane solvent is sulfolane.

References Cited by the Examiner UNITED STATES PATENTS 9/1961 Papadopoulos et a1. 208-325' 9/1965 Young 208-32] 

1. IN A PROCESS FOR THE EXTRACTION AND RECOVERY OF AROMATIC HYDROCARBONS WITH A SULFOLANE SOLVENT, FROM A LIQUID HYDROCARBON MIXTURE CONTAINING AROMATIC AND NON-AROMATIC HYDROCARBONS, WHEREIN THE SULFOLANE IS WATER-WASHED FROM AT LEAST ONE OF A SULFOLANE-CONTAINING NON-AROMATIC RAFFINATE AND A SULFOLANE-CONTAINING AROMATIC PRODUCT, THE IMPROVEMENT COMPRISING: (A) CONTACTING THE RESULTING SULFOLANE-CONTAINING WATERWASH IN A PRE-WASH ZONE WITH SAID HYDROCARBON FEED, THEREBY EXTRACTING THE SULFOLANE FROM THE SULFOLANECONTAINING WATER-WASH BY SAID FEED, AND (B) RECOVERNG A WATER PHASE OF SUBSTANTIALLY REDUCED SULFOLANE CONTENT. 